The present invention relates to methods used to fabricate semiconductor devices and more specifically to a method of fabricating a metal oxide semiconductor field effect (MOSFET) device featuring a channel region in a strained silicon region.
The ability to establish a channel region in a strained silicon region has allowed the performance of MOSFET devices to be enhanced. The increased mobility of carriers in the strained silicon region translates to increased drive currents thus enhanced device performance. Various options for creating the strained silicon region, or a silicon region under compressive strain, have been used such as forming the strained silicon layer directly on an underlying, relaxed silicon-germanium layer. Another option, practiced in the present invention, is the selective growth of relaxed silicon-germanium regions in an area of a semiconductor substrate to subsequently be used to accommodate a source/drain region. This option allows a strained silicon region, to be used to accommodate the MOSFET channel region, to be formed in a top portion of a semiconductor substrate located between the silicon-germanium regions. However, the selective growth of silicon-germanium has to be performed after definition of a conductive gate structure, and after insulator spacers have been defined on the sides of the conductive gate structure. The procedure used to grow silicon-germanium on regions of a semiconductor substrate wherein subsequent source/drain formation will occur, also results in silicon-germanium growth on the exposed top surface of a conductive gate structure. The growth of silicon-germanium on both type surfaces can however result in unwanted bridging of silicon-germanium across the insulator spacers possibly resulting in unwanted gate to substrate leakage or shorts.